This invention relates to melt spinning of synthetic fiber, filaments, yarn, ribbon and other extruded shapes when a quench stack is used. Particularly, this invention relates to the diffusion of quench air at the exhaust portion of the quench stack for quenching melt-spun synthetic fiber and the like. A typical quench stack is shown in U.S. Pat. No. 2,252,684 with diffusion at the exhaust portion shown at the bottom of FIG. 1 and FIGS. 2-4. Another known apparatus surrounded the freshly spun fiber or yarn with expanded metal covered with wire mesh, at the exhaust portion of the quench stack. This prior art apparatus improperly diffused the air around the freshly spun yarn because it did not allow for different flow rates of the air near the air exhaust as opposed to further from the air exhaust. Also, the wire mesh became blocked by loose yarn filaments.